Impregnating and bonding agent for textiles

ABSTRACT

Impregnating and bonding agent for textiles, comprising a mixture of a resorcinol-formaldehyde precondensate A, a rubber latex B and a melamine-formaldehyde resin C, impregnating process and reinforced rubber articles produced using the impregnates.

[0001] This invention relates to an impregnating and bonding agent fortextiles, especially for reinforcing materials which are vulcanized intorubber.

[0002] Textiles such as cords or fabrics based on rayon, polyamide,polyester, polyvinyl alcohol, glass fiber and aramid fiber which areused as reinforcements for rubber articles are customarily impregnatedwith latex baths which additionally contain resorcinol-formaldehyderesins. Such baths are known as resorcinol-formaldehyde-latex or RFLdips. Impregnation serves to improve the adhesion promotion betweenrubber and textile. Thus impregnated textiles have only in the outeredge zone (about {fraction (1/10)}-{fraction (1/30)} of the fiber orcord cross section) an impregnation layer which then promotes rubberadhesion during the vulcanizing operation. The interior of the fiber orcord is free of RFL impregnation, as a result of which the cord orfabric possesses good flexibility and has high fatigue resistance due tothe preserved filamentary structure.

[0003] Textiles based on polyester or aramid, which by their chemicalnature exhibit little adhesion to rubber, are customarily subjected totwo-bath impregnations. The first impregnating step, which is likewiseaqueous, is used to apply a small amount of an adhesion promoter such asblocked isocyanates or epoxy resins to the textile structure. This isfollowed by the impregnation with a resorcinol-formaldehyde latex.

[0004] RFL dips are frequently produced in-house by the processors fromthe ingredients. Resorcinol and formaldehyde are mixed in anamount-of-substance ratio of 1:1.5 to 1:2; after about 6 hours ofstorage in an alkaline medium at room temperature, the resin solutionformed is added to a latex containing natural rubber (NR),styrene-butadiene rubber (SBR) or vinylpyridine copolymer rubber (VP) ora mixture thereof. After a further 12 to 24 hours of “ripening” atconstant temperature, which is indispensable for uniform development ofadhesion, the bath thus produced is used for impregnating textiles.

[0005] Simpler handling is offered by precondensedresorcinol-formaldehyde resins, which are formulated together with therubber latex and aqueous formaldehyde solution to form RFL baths, inthat the ripening step can be omitted.

[0006] However, owing to their free formaldehyde content, neither typeof bath/dip is acceptable from an occupational hygiene standpoint.

[0007] It is an object of the present invention to provide impregnatingagents which lead to similar results for the adhesion between rubber andtextile reinforcements but contain little if any free formaldehyde.

[0008] This object is achieved by an impregnating and bonding agentwhich comprises a mixture of a resorcinol-formaldehyde precondensate, arubber latex and a melamine-formaldehyde resin.

[0009] The present invention accordingly provides an impregnating andbonding agent for textiles for improving rubber adhesion, comprising amixture of a resorcinol-formaldehyde precondensate A, a rubber latex Band a melamine-formaldehyde resin C.

[0010] The present invention further provides a process for producing atextile reinforcement having enhanced adhesion to rubber, whichcomprises said textile reinforcement being treated with an impregnatingand bonding agent comprising a mixture of a resorcinol-formaldehydeprecondensate A, a rubber latex B and a melamine-formaldehyde resin Cand subsequently dried.

[0011] The present invention further provides rubber articles havingenhanced adhesion between the textile reinforcement and the rubber,wherein said textile reinforcement has been impregnated with animpregnating and bonding agent comprising a mixture of aresorcinol-formaldehyde precondensate A, a rubber latex B and amelamine-formaldehyde resin C and has been vulcanized with a rubbermixture into a rubber article.

[0012] It is a further advantage of the invention that some of thecostly resorcinol precondensate can be replaced by an inexpensivemelamine resin. There is no longer any need to handle formaldehyde atall when making up the dips. It has also been determined that,surprisingly, the dips of the present invention have distinctly improvedstorage or aging stability compared with dips composed of resorcinolprecondensates and rubber latex, but not the melamine-formaldehyde resinwhich is present according to the present invention.

[0013] The impregnating and bonding agent of the present invention issubstantially free of formaldehyde. The mass fraction of freeformaldehyde in the impregnating and bonding agent is preferably lessthan 0.5%. The impregnating and bonding agent preferably comprisesresorcinol-formaldehyde precondensate A and melamine-formaldehyde resinC in a mass ratio (each based on solid resin) of 9:1 to 1:9, preferably7:3 to 3:7 and more preferably 4:6 to 6:4. The ratio of the sum total ofthe masses of the solids of resins A and C to the mass of the solid ofthe rubber in latex B (solids mass fraction or rubber content about 35to 45 cg/g) is preferably 1:1.5 to 1:15, more preferably 1:1.7 to 1:10and especially 1:2 to 1:9.

[0014] The resorcinol-formaldehyde precondensate A contains buildingblocks derived from formaldehyde and building blocks derived fromresorcinol, the amount-of-substance ratio of formaldehyde to resorcinolbeing 1:1.05 to 1:2, preferably 1:1.2 to 1:1.9 and especially 1:1.5 to1:1.8. It is essential to maintain a stoichiometric deficiency offormaldehyde; this keeps the resin at low molecular weight and soluble.Optionally, up to 10% of the resorcinol can be replaced by otherphenols, preferably dihydric phenols, provided the condensate preparedtherefrom remains soluble in water, ie when 1 g of resin is mixed with100 g of water at room temperature no insoluble residue visible to thenaked eye remains.

[0015] The latex B preferably contains a mass fraction of at least 5%,in the solids fraction, of building blocks derived from 2-vinylpyridine.Copolymerized singly or multiply unsaturated comonomers further include,in particular, styrene and butadiene. Latices of rubbers which containbuilding blocks of vinylpyridine are frequently known together as“vinylpyridine latex”. Other monomers customary in rubber chemistry canbe used as well, such as methylbutadiene, vinyltoluene, hexadiene andalso esters and other derivatives of acrylic acid. According to theinvention, it is possible to use mixtures of latices, provided at leastone mass fraction of 10% is used of a latex which contains buildingblocks derived from vinylpyridine. Frequently, blends with naturalrubber (NR) latex or styrene-butadiene rubber (SBR) latex are used. Ingeneral, however, it is also possible to use natural rubber latex, SBR,CR or NBR latex or suitable blends alone. Suitable latices are alsocommercially available from tire manufacturers or manufacturers ofindustrial rubber articles.

[0016] The melamine-formaldehyde resin C is an unetherified condensateof formaldehyde and melamine, the amount-of-substance ratio between thebuilding blocks derived from formaldehyde and melamine in the resin Cpreferably being between 1.5:1 to 6:1, more preferably between 1.8:1 to3.8:1 and especially between 2.1:1 and 3.2:1. The resins C arepreferably used as an aqueous solution of the pulverulent resins. Resinsare referred to as unetherified when not more than 10% of the N-methylolgroups are etherified.

[0017] It is also possible for the reinforcements used in the rubberindustry, for example fabrics or cords based on cotton, rayon,polyamides (nylon-6, nylon-6,6), polyester (polyethylene terephthalate),aramid (m-phenyleneisophthalamide, p-phenyleneterephthalamide) to becoated with a pre-dip prior to the impregnation with the disclosedimpregnating and bonding agent which contains resorcinol resin, pre-dipscustomarily containing blocked isocyanates or epoxides in the form ofaqueous dispersions. The passage through each bath is followed by athermal treatment (drying or curing). Combinations of epoxides andblocked isocyanates are also effective.

[0018] Textile reinforcements are, if necessary, impregnated with theabove-described pre-dip solution by means of a suitable impregnatingmachine. The cord or fabric tension must here be adjusted such that goodpenetration of the impregnating solution into the cord or fabricstructure is possible. Excess solution is removed by means of stripperdevices or suction nozzles after passage through the impregnating bath.After the moist textiles have been dried, they are customarily subjectedto a thermal treatment at 130 to 235° C. and preferably at 180 to 220°C., in the course of which the textiles are optionally tensilized.

[0019] The optionally thus pretreated textiles are treated with theabove-described resorcinol-formaldehyde rubber latex (RFL) solution ordip in a second actual impregnating step, which can follow immediatelyafter the pretreatment but may also be carried out after an interveningstorage period.

[0020] The solids mass fraction of the RFL dip is in the range 10 to 35%and preferably 20 to 30%. The choice of latex to be used should be madeaccording to the solid rubber into which the impregnated textile isvulcanized. After passing through the impregnating bath, the textile isinitially dried in a drying zone and subsequently cured at 130 to 235°C. The textile is then wound up and used for manufacturing theenvisioned articles.

[0021] Thus impregnated reinforcements can be used for producingV-belts, specifically raw-edge V-belts, transportation belts, hoses,membranes, automotive tires, in particular as a belt material. Cordswhich have been impregnated as described can further be subsequentlyprocessed into “cord fabrics”. The rubber articles produced using thethus prepared textiles can subsequently be cut to size, for exampleV-belts, transportation belts, hoses, membranes.

[0022] The invention will now be more particularly described withreference to examples. Hereinabove and hereinbelow, all % ages are massfractions (ratio of the mass of the substance in question to the mass ofthe mixture), unless otherwise stated. Concentrations in “%” are massfractions of the dissolved substance in the solution (mass of thedissolved substance divided by the mass of the solution).

EXAMPLES Example 1 Comparative

[0023] A conventional dip is prepared by mixing 200 g of a commerciallyavailable vinylpyridine latex (®Pliocord V 106 S, Goodyear Chemicals),22.5 g of a resorcinol precondensate (®Penacolite Resin R 50, 50%solution in water, Indspec Chemical Corporation), 6 ml of 25% aqueousammonia solution, 9 ml of 39% aqueous formaldehyde solution and 255 mlof completely ion-free water.

Example 2 Inventive

[0024] A dip according to the invention is prepared by mixing 200 g of acommercially available vinylpyridine latex (®Pliocord V 106 S, GoodyearChemicals), 11.25 g of a resorcinol precondensate (®Penacolite Resin R50, 50% solution in water, Indspec Chemical Corporation), 11.25 g of 50%aqueous solution of an unetherified melamine resin having anamount-of-substance ratio of formaldehyde to melamine of about 2.6:1, 6ml of 25% aqueous ammonia solution and 255 ml of completely ion-freewater.

Example 3 Testing of Adhesion to Aramid Cord; Impregnation with UnagedDips

[0025] A commercially available aramid cord (®Twaron, 1680 1 2 Z/S 250,Teijin Twaron BV) was impregnated with a dip as per example 1 and a dipas per example 2. The loading (mass increase due to impregnating agent,based on the mass of the impregnated cord after drying) was about 7.5%.The aramid cord was led through an impregnating tank, excess solutionwas stripped off and the impregnated cord was dried in a tubular oven at100° C. in the course of a passage time of 1 minute; curing was carriedout directly thereafter in a second tubular oven (residence time 2minutes, 200° C.)

Example 4 Testing of Adhesion to Aramid Cord; Impregnation with AgedDips

[0026] Example 3 was repeated except that the two dips were stored atroom temperature (20° C.) for 14 days after preparation.

[0027] Adhesion Testing:

[0028] The adhesion test was carried out as a T-test. An impregnatedcord was placed between two rubber strips (composition see table 1) ofequal thickness and the structure was vulcanized at 145° C. for 45minutes. Before testing, the test specimens were stored at roomtemperature for 24 hours. A tensile tester was used to pull the cordsout of the composite at an extension rate of 300 mm/min. The results aresummarized in table 2. The recipe of the rubber used was: TABLE 1 Rubberrecipe Mass in g per Ingredients 100 g of rubber Natural rubber (NR) 100Stearic acid 0.8 ® Vulkanox HS 0.8 (TMQ, 2,2,4-trimethyl-1,2-dihydroquinoline, polymerized) ® Vulkanox 4010 NA 0.6 (IPPD;N-isopropyl-N′-phenyl- p-phenylenediamine) Zinc oxide 7.0 ® Naftolen V4055 (plasticizer oil) 7.0 Carbon black 43.0 Sulfur 2.8 ® Rhenogran CTP80 (N- 0.5 cyclohexylthiophthalimide) ® Vulkacit LDA (ZDEC, zinc 0.7diethyldithiocarbamate)

[0029] The measured result reported is the force per unit length atwhich yarn pullout was observed. TABLE 2 Adhesion to aramid(length-specific pullout force F_(L) in N/cm) Dip of example 1 2 F_(L)(unaged) in N/cm 111 109 F_(L) (aged) in N/cm 89 140

[0030] Whereas a conventional dip (resorcinol precondensate andformaldehyde together with vinylpyridine latex) gave an acceptableadhesion value when freshly prepared, the adhesion value decreases byabout 20% to an unacceptable level after this dip has been stored for 14days. In contrast, the dip according to the present invention, whichstarts from approximately the same fresh value, improved on storage byabout 27% in terms of adhesion performance. The dips according to thepresent invention can therefore remain in the baths even in the event ofdisruptions to the production process; the results do not deteriorate asa result. In the case of conventional dips, however, the baths have tobe refilled after disruptions to the production process.

Example 5 Testing of Adhesion to Polyester Cord

[0031] Example 3 was repeated except that the aramid cord was replacedby a polyester cord (1670 1 2 Z/S 340, KoSa GmbH & Co. KG). To test thestability in storage, a comparison was arranged as in example 4 betweenfreshly prepared dips (as per examples 1 and 2) and dips which, beforethe impregnating operation, were stored at room temperature for 14 daysafter preparation.

[0032] The predrying was carried out as above at 100° C. for 1 minute,and the curing was carried out at 230° C. for 70 seconds. The results ofthe adhesion test, which was carried out as described above, aresummarized in table 3. TABLE 3 Adhesion to polyester (length-specificpullout force F_(L) in N/cm) Dip of example 1 2 F_(L) (unaged) in N/cm165 160 F_(L) (aged) in N/cm 126 153

[0033] There is no improvement in adhesion on storage, but, within themargin of error, the adhesion provided by the dip according to thepresent invention remains virtually unchanged (−4%), while in the caseof the conventional dip (example 1) the adhesion decreases by about 24%after storage.

Example 6 Testing of Aging at Elevated Temperature

[0034] The dip of example 2 according to the present invention was usedto carry out further aging tests. The following adhesion values onpolyester cord (as in example 5) were determined for the storageconditions specified in table 4: TABLE 4 Adhesion to polyester(length-sp cific pullout force F_(L) in N/cm) Storage F_(L) in N/cmdirectly after preparation 160 9 hours; 50° C. 166 18 hours; 50° C. 16214 days; room temperature (20° C.) 153 9 hours; 50° C. + 14 days; 20° C.142 18 hours; 50° C. + 14 days; 20° C. 140

[0035] It was found that the system according to the present inventionprovides advantages even on storage at comparatively high temperatures.

What is claimed is:
 1. An impregnating and bonding agent for textiles,comprising a mixture of a resorcinol-formaldehyde precondensate A, arubber latex B and a melamine-formaldehyde resin C.
 2. An impregnatingand bonding agent for textiles as is claimed in claim 1, wherein saidresorcinol-formaldehyde precondensate A and said melamine-formaldehyderesin C are present in a mass ratio (each based on solid resin) of 9:1to 1:9.
 3. An impregnating and bonding agent for textiles as is claimedin claim 1, wherein the ratio of the sum total of the masses (solidsfraction in each case) of said resins A and C to the mass of said rubber(solids fraction) in said latex B is 1:1.5 to 1:15.
 4. An impregnatingand bonding agent for textiles as is claimed in claim 1, wherein theamount-of-substance ratio in said resorcinol-formaldehyde precondensateA of the building blocks derived from formaldehyde and the buildingblocks derived from resorcinol is 1:1.05 to 1:2.
 5. An impregnating andbonding agent for textiles as is claimed in claim 1, wherein theamount-of-substance ratio in said melamine-formaldehyde resin C betweenthe building blocks derived from formaldehyde and from melamine isbetween 1.5:1 to 6:1.
 6. An impregnating and bonding agent for textilesas is claimed in claim 1, wherein said latex B contains a mass fractionof at least 5%, in the solids fraction, of building blocks derived from2-vinylpyridine.
 7. An impregnating and bonding agent for textiles as isclaimed in claim 1, wherein said latex B is a mixture of latices, atleast one mass fraction of 10% being present of a latex which containsbuilding blocks derived from vinylpyridine.
 8. A process for producing atextile reinforcement having enhanced adhesion to rubber, whichcomprises said textile reinforcement being treated with an impregnatingand bonding agent as claimed in claim 1 and subsequently dried.
 9. Arubber article having enhanced adhesion between a textile reinforcementand said rubber, wherein said textile reinforcement has been impregnatedwith an impregnating and bonding agent comprising a mixture of aresorcinol-formaldehyde precondensate A, a rubber latex B and amelamine-formaldehyde resin C and has been vulcanized with a rubbermixture into a rubber article.